Recently, the characteristics of power electronic devices have been improved significantly. Power electronic devices with high-voltage rating, high-current rating, and high switching speeds have been developed due to the improvement of semiconductor manufacturing techniques. Power electronic devices are applied in electric power equipment, such as switching power supplies, uninterruptible power supplies, motor drivers, arc furnaces, trolley cars, battery chargers, lighting appliances etc. For example, converters are well known in the field of electronics, such as DC-to-DC, DC-to-AC, AC-to-DC or AC-to-AC converters. Such circuitry or devices are typically employed to convert from one DC or AC voltage to another DC or AC voltage.
Typically, there are several kinds of power systems using the converters, such as central power system (CPS) or distributed power system (DPS). Refer to FIG. 1. FIG. 1 is a system block diagram showing a conventional central power system. In the central power system, a single input power source 911 is electrically connected to a DC-to-DC converter 912 and a plurality of loadings 913 (such as electronic devices). The input power source 911 may be a DC power source. The DC-to-DC converter 912 is employed to convert from one DC voltage level to another DC voltage level. Therefore, the input power source 911 can supply power to the loadings 913. However, there are some disadvantages in the central power system, such as high current stress on devices, poor reliability and difficulty in power maintenance etc.
Refer to FIG. 2. FIG. 2 is a system block diagram showing a conventional distributed power system. In the distributed power system, a single input power source 921 is electrically connected to a plurality of DC-to-DC converters 922 and a plurality of loadings 923 (such as electronic devices), wherein each of the DC-to-DC converters 922 is electrically connected to each of the loadings 923, thereby supplying power to the loadings 923. There are some advantages in the distributed power system, such as lower current stress on devices, supporting of N+1 redundancy, ease to maintenance and customization using standardized module etc. However, when the single input power source 921 is broken-down or fails to supply power, the whole distributed power system would be useless.